Transcript of "Introduction to psychopharmacology"
INTRODUCTION TO PSYCHOPHARMACOLOGY<br />HYACINTH C. MANOOD, MD, FPPA<br />
GENERAL PRINCIPLES:<br />Classification<br />Pharmacological Actions<br />Pharmacodynamics<br />Pharmacokinetics<br />Metabolism and Excretion<br />Clinical Guidelines<br />Special Treatment Considerations<br />Adverse Effects<br />Discontinuation or Withdrawal Syndrome<br />Intoxication or Overdose<br />
CLASSIFICATION<br />Psychotropic, psychoactive, or psychotherapeutic drugs<br />4 traditional categories: <br /> 1)antipsychotics, 2)antimanic or mood stabilizers, 3)antidepressants,<br /> 4)antianxiety or anxiolytics<br />
Many drugs of one class are used to treat disorders previously assigned to another class.<br />Drugs from all four categories are used to treat disorders previously not treatable by drugs.<br />Some non-psychiatric drugs can treat a variety of psychiatric disorders effectively but do not fit easily into the traditional classification.<br /> e.g., Clonidine, Gabapentin, Propanolol<br />Some descriptive psychopharmacological terms overlap in meaning. <br />eg. Anxiolytics also have sedative effects<br />
Pharmacological Actions<br />Pharmacodynamics<br />Effects of the drug on the biological activities of the body.<br />Receptor mechanism<br />Therapeutic index<br />Dose response curve<br />Development of tolerance, dependence, and withdrawal phenomena<br />
Receptor– the cellular component to which the drug binds and through which the drug initiates its pharmacological effects on the body.<br />Dose Response Curve – plots the drug concentration against the effect of the drugs. <br />POTENCY – the relative dose required to achieve certain effects.<br />CLINICAL EFFICACY – the max clin. Response achievable by administration of a drug<br />
Therapeutic index - a relative measure of the toxicity or safety of a drug<br /> - ratio of the median toxic dose to median effective dose.<br />median toxic dose – dose at which 50% of patients experience a specific toxic effects<br /> median effective dose – dose at which 50% of patients experience a specified therapeutic effect.<br />
Pharmacokinetics<br />How the body handles the drug.<br />Absorption :<br />Orally administered drugs dissolve in GIT fluids and are then absorbed in the blood – then reach the brain.<br />Parenteral administration more rapid than oral<br />Depot preparations – emulsified in an insoluble carrier matrix sustaining the drug’s gradual release through IM administration<br />IV administration is the quickest route but carries the highest risk of sudden and life-threatening adverse effects.<br />
Distribution and Bioavailability<br />Protein-bound – bound to plasma proteins<br />Free – if the circulate unbound<br />Only the free fraction can pass thru the BBB<br />High CBF, high lipid solubility, and high receptor affinity promote therapeutic actions of the drug<br />Volume of distribution- measure of apparent space in the body available to contain the drug.<br />Bioavailability - the fraction of the total amount of administered drug that can be subsequently recovered from the bloodstream.<br />
Metabolism and Excretion<br />4 major metabolic routes:<br /> 1.)oxidation 3.)hydrolysis<br /> 2.)reduction 4.)conjugation<br /> - yields inactive metabolites that are more readily excreted<br /> - transform inactive prodrugs into therapeutically active metabolites.<br /><ul><li> The LIVER is the principal site of metabolism
BILE, FECES, and URINE are major routes of excretion</li></li></ul><li>Half-life - the amount of time it takes for metabolism and excretion to reduce a particular plasma concentration into half.<br />First-pass effect – initial metabolism of orally-administered drugs within the portal circulation of the liver;<br />Clearance – measure of the amount of drug excreted from the body in a specified period of time.<br />
CYTOCHROME P450 ENZYMES<br />Most psychotropic medications are oxidized by hepatic CYP enzyme system.<br />Act primarily in ER of hepatocytes and cells of the intestines.<br />Cellular pathology in these sites may affect the efficiency of drug metabolism by the CYP system<br />Certain drug combinations should be done so with caution or should be avoided.<br />Long half-lives prolong inhibition of CYP system<br />
Clinical Guidelines:<br />Choice of Drug<br />Diagnosis and identification of target symptoms<br />Drugs currently taken and recently discontinued<br />Supotimal dosage of appropriate drugs<br />
Special Treatment Considerations<br />A. GERIATRIC PATIENTS <br /> -older persons may be especially susceptible to adverse effects<br /> -slow metabolism<br />B. CHILDREN<br /> - small volume of distribution<br /> - higher rate of metabolism<br />
C. PREGNANT AND NURSING WOMEN<br /> - the two most teratogenic drugs in psychopharmacology are LITHIUM and the ANTICONVULSANTS.<br />Lithium – birth anomalies like Ebstein anomaly<br />Anticonvulsants – fetal craniofacial and neural tube anomalies<br />- Risk of teratogenicity is lowered by administration of FOLIC ACID<br />
D. PERSONS WITH HEPATIC AND RENAL INSUFFICIENCY:<br /> - drugs may accumulate to toxic concentrations.<br /> - reduced dosage, usually half the recommended dose.<br /> - monitor plasma drug concentrations<br />E. PERSONS WITH OTHER MEDICAL ILLNESSES<br /> - increased sensitivity to adverse effects<br /> - altered metabolism<br /> - interactions with other medications<br />
Adverse Effects<br />Sexual dysfunction – most commonly associated with the use of SSRI.<br />Tx. Shift to Nefazodone or Bupoprion<br />Anxiety, Akathisia, and Insomnia – SSRI and antipsychotics.<br />Tx. Benzodiazepines, Anticholinergics, shift to non SSRI antidepressants<br />GI upset and Diarrhea – Sertraline most likely to cause loose stools, Fluvoxamine most likely to cause nausea;<br />Tx. Begin with low dose, adm drug after eating, BRAT diet.<br />
Headache – SSRI; Tx: ovr the counter analgesics<br />Anorexia – SSRI<br />Weight gain – atypical antipsychotics bec. of disturbance in glucose and insulin metabolism<br /> TX. Diet<br />Somnolence – desirable adverse effect<br />Dry Mouth – caused by blockade of muscarinic acetylcholine receptors<br />Tx. Chew sugarless gum, 1% solution of Pilocarpine as mouthwash 3x a day<br />
Urinary Retention – anticholinergic activity<br />Tx. Betanechol 10 -30 mg once or twice daily<br />Constipation – Tx. Laxatives, Betanechol<br />Orthostatic hypotension – caused blockade of a1-adrenergic receptors.<br /> TX. Instruct patient to get up slowly and sit down immediately if dizziness is experienced.<br /> Avoid caffeine<br /> Drink at least 2 Liters of fluids daily<br /> adding salt to food<br /> reassess dosages of antihypertensive meds<br />
Discontinuation Syndrome – transient emergence of mild symptoms upon the discontinuation or reduction of dosage <br />SSRI . TCAC’s, Lithium, DRA, Benzodiazepines<br />Lithium – rebound mania<br />DRA – tardivedyskinesia<br />Benzodiazepines – anxiety and insomnia<br />SEROTONIN DISCONTINUATION SYNDROME <br />Agitation, nausea, dysequilibrium and dysphoria<br />Symptoms are time-limited<br />Minimized by gradually reducing the dosage<br />
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